1. Field of the Invention
This invention concerns a method for forming a prescribed pattern of, e.g., a wiring layer by etching, on a semiconductor device.
2. Description of the Prior Art
Conventionally, for etching a semiconductor substrate, a Reactive Ion Etching (RIE) is utilized using a photoresist pattern formed on the semiconductor substrate as a mask.
FIG. 1 is a diagram for explaining a problem which is present in a conventional process for forming a pattern of submicron dimensions using a conventional exposure and development technique. Namely, in the case where the width between the adjacent pattern is relatively wide, e.g. 1.0 .mu.m, a desired pattern may be obtained by the conventional technique. However, in the case where the width is 0.8 .mu.m (e.g., between the photoresist pattern 12 and 13), some undeveloped photoresist remains on the substrate 10, since the bottom portion of the photoresist is not sufficiently exposed even if the upper portion is clearly patterned. Thus, it is difficult to use the photoresist pattern 12 and 13 as a mask in a subsequent etching process.
FIGS. 2A and 2B are diagrams for explaining a problem in a conventional process for forming a prescribed pattern of a high reflective metal layer 21 in a recessed portion 24 of a semiconductor substrate 20. In the conventional process, a material of high reflectivity, such as a tungsten silicide 21, is formed. A photoresist layer 23 is then formed thereon. (FIG. 2A) Next, an exposure and a development are carried out to form a photoresist pattern 23a and 23b. By this process, a desired pattern 23a and 23b of photoresist may be formed on a flat surface of the substrate 20. However, at the level difference portion 24, the reflected light from the angled surface 22 of the metal layer 21 exposes the photoresist 23 in the recess. Thus, the desired pattern illustrated by the dotted line 23c can not be obtained, and a photoresist pattern 23d may result instead. Therefore, it is also difficult to use the pattern 23d as a mask to etch the metal layer 21 accurately.